boards: stm32f030_demo: enable stm32flash in addition to OpenOCD
boards: stm32f030_demo: enable stm32flash in addition to OpenOCD

This commit makes it possible to use stm32flash for flashing (with west)
the STM32F030 Demo Board. OpenOCD is still the default, so in order to
use stm32flash, one must invoke ‘west flash’ with ‘-r stm32flash’.

Signed-off-by: Grzegorz Szymaszek <d5fcac35f7890f8e382f3bebb7ef93d1da798a00@short.pl>

galak/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,finikorg/zephyr,nashif/zephyr,Vudentz/zephyr,galak/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,Vudentz/zephyr,Vudentz/zephyr,finikorg/zephyr,Vudentz/zephyr,Vudentz/zephyr,finikorg/zephyr,galak/zephyr,finikorg/zephyr,galak/zephyr